Cold chamber die-casting piston

ABSTRACT

The finding relates to a piston for cold chamber die-casting machines that comprises a steel body and at least one sealing band in copper alloy mounted around the body into a respective housing in back position with respect to the piston head. At least two channels are provided on the outside surface of the piston comprised between head and sealing band, for an inflow on the melted metal under the same band. When such metal solidifies, it creates a thickness that radially pushes the band outwards, thus compensating for its wear.

SCOPE OF THE INVENTION

[0001] The present finding relates to die-casting machines. In particular, it refers to a piston of a press for die-casting.

PRIOR ART

[0002] Die-casting machines can be of the hot chamber or cold chamber type.

[0003] An injection piston is commonly used in hot chamber die-casting machines, having a steel body with sharp or slightly bevelled edge head carrying one or usually two copper alloy sealing bands spaced in parallel from one another and from the piston head.

[0004] In cold chamber die-casting machines, both the use of an injection piston with a copper alloy or steel body without outside sealing bands and with an optional peripheral head step and/or bevel, and the use of an injection piston with a copper alloy body and an outside sealing band arranged astride of a collar at the piston head, are known.

[0005] Such known embodiments, however, exhibit the disadvantage of a relatively quick loss of seal, and thus, a reduction of the piston efficiency and life following the wear, especially of the sealing band closer to the piston head, which is also increased by thermal deformations of the system, such as ovalization of the piston container. In this case, the seal can only be restored by replacing the worn band or bands.

PURPOSES AND SUMMARY OF THE FINDING

[0006] A purpose of the present finding is that of providing a piston for cold chamber die-casting which should be more efficient and with a longer life than the current ones, and which should thus allow reducing the operating costs of die-casting machines.

[0007] Another purpose of the finding is that of proposing a piston provided with sealing bands in copper alloy which, even though becoming worn, should be stressed to rearrange radially and conform to the thermal deformations, so as to not impair the piston life and efficiency.

[0008] Such purposes are achieved by a piston for cold chamber die-casting machines comprising a steel body having a head with or without peripheral bevel and at least one sealing band in copper alloy arranged around the body into a respective housing obtained in back position with respect to the head, and where at least two channels are obtained on the outside surface of the piston comprised between head and band, suitable for placing the piston head in communication with the annular housing of the band, for an inflow of metal under the same band.

[0009] In this way, when the metal flowing to the housing solidifies, it creates a continuous thickening which radially pushes the band outwards, thus progressively recovering its wear, conforming it to the possible deformations of the container of the piston and thereby protecting the latter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Further features of the finding shall appear more clearly from the following description, made with reference to the attached exemplificative and non-limiting drawings. In such drawings:

[0011]FIG. 1 shows a longitudinal section view of the piston according to the finding; and

[0012]FIG. 2 shows a top view of the piston with compensation channels.

DETAILED DESCRIPTION OF THE INVENTION

[0013] Said drawings show a piston 10 having a body 11 and at least one, or better two external sealing bands 12,12′, in copper alloy. The piston body has a head 13 orthogonal to the piston axis, which can be provided with a peripheral bevel 14, as in the illustrated example, or a sharp or rounded edge.

[0014] The sealing bands 12,12′ are arranged into respective housings 15,15′ obtained around body 11.

[0015] According to the finding, at least two channels 16 are obtained on the outside surface of the piston body comprised between head 13 and the band 12 closer to it, and they place the bottom of housing 15 of the band in communication with the piston head. Through said channels, the melted metal can flow into housing 15 under band 12, so as to create a continuous thickening that compensates for the band thinning caused by its wear following the use of the piston and the thermal deformations of its container.

[0016] In this way, the piston exhibits a longer seal and efficiency independently of the wear degree of the copper alloy band. 

1. Piston for cold chamber die-casting machines comprising a steel body and at least one sealing band in copper alloy mounted around the body into a respective housing in back position with respect to the piston head, characterised in that it exhibits at least two channels obtained on the outside surface of the piston comprised between head and sealing band, suitable for placing the piston head in communication with the band housing, for an inflow of the melted metal under the same band which when solidifies, creates a thickness that radially pushes the bad outwards, thus compensating its wear.
 2. Piston according to claim 1, wherein its body, at the height of said channel, exhibits a peripheral bevel of tapering of the piston portion adjacent its head.
 3. Piston according to claim 1, wherein its body, at the height of said channels, exhibits a cylindrical peripheral surface.
 4. Piston according to claim 1 and 2 or 3, wherein the body is provided with two outside sealing bands and exhibits a plurality of longitudinal channels between its head and the housing of the sealing band that is closer to the head. 